1. Field of the Invention
The present invention relates to a production method of xylylenediamine by a continuous two-stage hydrogenation of a dicyanobenzene compound.
2. Description of the Prior Art
The production method of xylylenediamine by the hydrogenation of a corresponding dicyanobenzene compound in the presence of a catalyst is well known in the art. For example, Japanese Patent Publication No. 38-8719 discloses an autoclave batch-wise hydrogenation of a dicyanobenzene compound into the corresponding diamine in an alcohol in the presence of Raney nickel or Raney cobalt together with a trace amount of an caustic alkali. Japanese Patent Application Laid-Open No. 54-41804 discloses an autoclave batch-wise hydrogenation of a dicyanobenzene compound into the corresponding diamine in a mixed solvent of a lower alcohol and a cyclic hydrocarbon in the presence of a hydroxide or alkolate of alkali or alkaline earth metal together with a Raney nickel of Raney cobalt catalyst. Japanese Patent Application Laid-Open No. 6-121929 discloses an autoclave batch-wise hydrogenation of an isophthalonitrile compound into the corresponding diamine in a methanol-ammonia solvent in the presence of a Rh—Co-containing catalyst.
Japanese Patent Publication No. 53-20969 discloses a liquid-phase catalytic reduction of a dicyanobenzene compound by hydrogen in the presence of a Ni—Cu—Mo-containing catalyst. The catalytic reduction is performed by a fixed-bed continuous hydrogenation in the working examples. Japanese Patent Application Laid-Open No. 56-83451 discloses a production method of diamine in the presence of a slurry-bed Rh—Co-containing catalyst. “Process Handbook”, Japan Petroleum Institute, 1978 discloses an industrial production process in which the starting nitrile is introduced into a hydrogenation reactor together with a solvent and a catalyst and hydrogenated therein under slurry conditions.
To yield xylylenediamine efficiently by hydrogenation, it is required to increase the progress of the hydrogenation of nitrile group into aminomethyl group (conversion of nitrile group) and minimize the amounts of non-reacted dicyanobenzene and intermediate cyanobenzylamine generated by the hydrogenation of only one of the nitrile groups. It is desirable that the concentration of cyanobenzylamine in the liquid mixture after hydrogenation is low, because the difference in the boiling points of cyanobenzylamine and the corresponding xylylenediamine is generally small to make the separation thereof by a usual distillation difficult. Therefore, it is preferred for the efficient production of xylylenediamine to proceed the hydrogenation into xylylenediamine efficiently and to minimize the concentration of cyanobenzylamine after the hydrogenation by increasing the conversion of nitrile groups, thereby making the purification of xylylenediamine easy.
One of the methods for increasing the conversion of nitrile groups is to prolong the contact time with a catalyst. To prolong the contact time, it is required for a fixed-bed reaction to use a large amount of catalyst in an increased size reactor while not changing the flow rate, and required for a batch-wise reaction to prolong the reaction time. These methods, however, are inexpedient for industrial production because of a poor use efficiency of catalyst, increased reactor costs, catalyst costs and a lowered productivity.
Another method for increasing the conversion of nitrile groups is to increase the reaction temperature. By increasing the reaction temperature, the amount of the dicyanobenzene compound remaining not reacted is reduced and the generation of cyanobenzylamine is prevented. However, high reaction temperatures sometimes increase unfavorable side reactions such as deamination and condensation to lower the yield of xylylenediamine.
As described above, in the known methods of hydrogenating the dicyanobenzene compound, it is difficult to sufficiently prevent the generation of cyanobenzylamine without deteriorating the use efficiency of catalyst and the yield of xylylenediamine. Thus, in the industrial hydrogenation of dicyanobenzene, it is practically impossible to completely prevent the generation of cyanobenzylamine. Therefore, to obtain a highly pure xylylenediamine with a low content of cyanobenzylamine, the conventional technique requires plural purification steps after the hydrogenation of the dicyanobenzene compound: a removal of cyanobenzylamine, which is difficult to separate by distillation, form xylylenediamine by a specific method such as an alkali treatment (Japanese Patent Publication No. 45-14777) and a treatment with iron-containing catalyst (Japanese Patent Application Laid-Open No. 57-27098); and a subsequent distillation.
Recently, a highly pure xylylenediamine with a low content of cyanobenzylamine is demanded particularly in the use thereof as the raw material of isocyanates. In such a use, the content of dicyanobenzene in xylylenediamine is required to be 0.02% by weight or less. Therefore, there has been a demand for developing an industrially advantageous method of producing a highly pure xylylenediamine with a low content of cyanobenzylamine.
As described above, in the production of xylylenediamine by the hydrogenation of the dicyanobenzene compound, it has been difficult to sufficiently prevent the generation of cyanobenzylamine without deteriorating the use efficiency of catalyst and the yield of xylylenediamine. Therefore, it has been required, particularly for the production of a highly pure xylylenediamine with a small content of cyanobenzylamine, to purify xylylenediamine by plural steps: a removal of cyanobenzylamine by a specific treatment and a subsequent distillation.